This application claims priority to an application entitled xe2x80x9cHigh Efficiency Burner for Over-Cladding and Apparatus For Over-Cladding Large Diameter Optical Fiber Pre-form Using The Samexe2x80x9d filed with the Korean Industrial Property Office on Dec. 22, 1999 and there duly assigned Serial No. 99-56746.
1. Field of the Invention
The present invention relates generally to an apparatus for fabricating an optical fiber pre-form. More particularly, the present invention relates to a high efficiency burner and an apparatus for over-cladding a large diameter optical fiber pre-form using the same, in which a first pre-form is inserted into an inside of a thick quartz tube, to be heated during an over-cladding processing.
2. Description of the Related Art
In general, an optical fiber comprises a core having a predetermined index of refraction therein, and a cladding having a refraction index lower than that of the core for making a total reflection of incident lights. A method for fabricating the optical fiber comprises the steps of fabricating an optical fiber pre-form and drawing the fabricated optical fiber into one strand of optical fiber. Thereafter, the drawn optical fiber is coated to become a complete strand of optical fiber.
On the other hand, an over-cladding or an over-jacketing process is conducted to the fabricated optical fiber pre-form to draw an optical fiber having a larger diameter. Specifically, the over-cladding or over-jacketing process is conducted to the fabricated first cylindrical optical fiber pre-form with a tubular second quartz tube, thereby completing the optical fiber pre-form having a larger diameter. Here, a chemical vapor deposition or a sol-gel process is widely used for fabricating the second quartz tube, namely a silica-based glass using a fumed silica.
The over-cladding process fabricates an optical fiber pre-form of a larger diameter by inserting a first pre-form, which is manufactured by means of chemical vapor deposition or other methods for fabricating a pre-form, into the inside of a thick quartz tube, and then heating and sealing the same with a heat source. This process enlarges the cladding layer, thereby producing a pre-form having a larger diameter promising high productivity.
The heat source heating the second quartz tube during the over-cladding of the optical fiber pre-form is generally used as a burner using hydrogen and oxygen gas.
Referring to FIG. 1, the heat source is a burner using hydrogen and oxygen gas and has a ring shape, part of which is shown.
Further, FIG. 1 is a front view illustrating an inner surface, i.e., a surface at which a flame is discharged, of the burner 130 opposite to a quartz tube. The burner 130 has burner bodies 134 between burner covers 132 with hydrogen and oxygen dischargers 136 and 138 arranged between the burner bodies 134. The hydrogen and oxygen dischargers 136 and 138 are continuously provided with hydrogen and oxygen gas, so as to heat the surface of the second quartz tube. The hydrogen discharger 136 signifies an inside of each tip 139, while the oxygen discharger 138 signifies an outside of the tip 139. In addition, hydrogen and oxygen mass flow controllers (MFC) 140 and 142 are included, respectively, in the burner 130, for controlling a mass flow of the hydrogen and oxygen gas.
Here, the larger a thickness or a scale of the over-cladding quartz tube is, the higher a required heat capacity is. If a heat is first applied to an outer surface of the quartz tube, in order to perform an over-cladding on the first pre-form with the second quartz tube, the heat is conducted to the quartz tube, converging on a predetermined region therein, whereby the hottest region, referred to as a xe2x80x9chot zone,xe2x80x9d is formed in the predetermined region of the quartz tube. The heat is conducted from the hot zone to an inside of the second quartz tube, which is condensed and melted into the first pre-form to produce a second pre-form. Thus, if the second quartz tube subject to the over-cladding is thick, the burner should have a size in conformity of a periphery of the second quartz tube, so as to achieve an efficient heat transfer to the inside thereof. In addition to this, a provision of a fuel such as hydrogen and oxygen gas is preferably increased to enhance a heat capacity.
However, as the quartz becomes thicker, the amount of fuel which is required is drastically increased. Further, while the heat value is focused on the hot zone, the hottest region among regions in the outer surface of the quartz tube heated by the burner and then the hot zone is condensed, even before the hot zone is not condensed, there sometimes generates an occasion, in which the surface of the quartz tube runs down due to its deterioration of viscosity. In this regard, an intensive heating on the hot zone by enhancing the amount of fuel has a limit.
Further, there is a way to extend a fuel-sprayed region for enlarging the hot zone. In this case, an equal provision of fuel such as hydrogen and oxygen gas is difficult to be achieved, thereby resulting in an irregular heat provision. As a consequence, a uniform over-cladding is not assured.
It is, therefore, an object of the present invention to provide a process for over-cladding an optical fiber pre-form, by which a double-clad structured burner is used, so as to enlarge a hot zone on an equal basis and therefore improve a thermal efficiency as well as securing a uniform and efficient over-cladding.
It is another object of the present invention to provide a process for over-cladding an optical fiber pre-form, by which an equal and highly efficient heating is applied particularly during an over-cladding of a thick quartz tube, so as to curtail the time for over-cladding, thereby serving to promote productivity.
It is further another object of the present invention to provide a process for over-cladding an optical fiber pre-form, through which a double-clad structured burner is used, so as to provide means additionally operable with a different heating value, if necessary.
It is still another object of the present invention to provide a process for over cladding an optical fiber pre-form, by which a uniform fuel provision is carried out, so as to prolong a durability of burner tips.
To achieve the above objects, there is provided a burner according to the present invention. The burner heating an optical fiber pre-form includes burner covers, burner bodies positioned between the burner covers, and fuel dischargers arranged in at least two rows between the burner bodies and divided by a partition.
Accordingly, the apparatus for over-cladding the optical fiber pre-form according to the present invention, which performs an over-cladding on an optical fiber pre-form with a quartz tube, includes: upper and lower fixing chucks mounted on upper and lower sides of a tower; a first optic fiber pre-form having a handle rod connected to one end thereof so as to be fastened to the upper and lower fixing chucks, and having a supplementary support quartz tube connected to the other end thereof so as to be fastened to the lower fixing chuck; a second quartz tube inserted into the first optic fiber pre-form; and a hydrogen and oxygen burner including fuel dischargers including an oxygen discharger and a hydrogen discharger, at least double-clad structured and divided by a partition, thereby enlarging the hot zone in the quartz tube.